Electronic endoscope with brightness adjustment function

Abstract

An electronic endoscope has a video-scope with an image sensor, a light source that emits illuminating-light to illuminate an object, an image sensor driver, a luminance detector, one rotary shutter, and a brightness adjuster. The luminance detector detects a luminance of an object image on the basis of image-pixel signals read from the image sensor. The rotary shutter has a light-transmitting portion that transmits the illuminating light, and a shield portion that blocks the illuminating light. The brightness adjuster controls the rotary shutter to adjust an irradiation-interval of the illuminating-light in accordance with a charge accumulation interval. The brightness adjuster shifts a rotation-phase of the rotary shutter by changing a rotation-speed on the basis of the detected luminance, so as to maintain a brightness of the object image at a proper brightness.

1. An electronic endoscope comprising:
 a video-scope with an image sensor; 
 a light source that emits illuminating-light for illuminating an object; 
 an image sensor driver that outputs pulse signals for transferring charges accumulated in said image sensor in each field/frame interval, said image sensor driver outputting a pulse signal for discarding accumulated charges on the basis of a charge accumulation interval; 
 a luminance detector that detects a luminance of an object image on the basis of image-pixel signals read from said image sensor; 
 a single rotary shutter comprising a light-transmitting portion that transmits the illuminating-light, and a shield portion that blocks the illuminating light, said single rotary shutter being configured to rotate while the light-transmitting portion and the shield portion alternately cross a light-path of the illuminating-light; and 
 a brightness adjuster that controls said rotary shutter to change an irradiation-interval of the illuminating-light in a field/frame interval in accordance with the charge accumulation interval, said brightness adjuster shifting a rotation-phase of said rotary shutter by changing a rotation-speed of the rotary shutter on the basis of the detected luminance, so as to maintain a brightness of the object image at a proper brightness. 
 
   
   
     2. The electronic endoscope of  claim 1 , wherein said image sensor driver adjusts the charge accumulation interval to the irradiation interval in one field/frame interval in accordance with the shifted rotation-phase. 
   
   
     3. The electronic endoscope of  claim 1 , further comprising a light source controller that is capable of selectively setting an intensity level of illuminating light to one of a normal level required for illuminating an object and a low level adjacent to zero level, said light source controller setting the normal level for the irradiation interval, and setting the low level for an other interval. 
   
   
     4. The electronic endoscope of  claim 1 , wherein said light-transmitting portion comprises a pair of aperture portions, said pair of aperture portion being opposite each other and each extending circumferentially by a quarter-circle. 
   
   
     5. The electronic endoscope of  claim 1 , wherein said light-transmitting portion comprises an aperture portion, said aperture portion extending circumferentially by a semi-circle. 
   
   
     6. The electronic endoscope of  claim 1 , wherein said light-transmitting portion comprises R, G, and B color filters extending circumferentially and spaced from one another at regular intervals. 
   
   
     7. The electronic endoscope according to  claim 1 , wherein said brightness adjuster changes an illumination time from a start to an end of the field/frame interval by shifting a rotation phase of said rotary shutter. 
   
   
     8. An apparatus for adjusting a brightness of an object image in an electronic endoscope, comprising:
 a luminance detector that detects a luminance level of an object image on the basis of image-pixel signals that are read from an image sensor of a video-scope successively; 
 a single rotary shutter comprising a light-transmitting portion and a shield portion, said single rotary shutter being configured to rotate while the light-transmitting portion and the shield portion alternately cross a light-path of the illuminating-light; and 
 a brightness adjuster that controls said rotary shutter to adjust an irradiation interval of the illuminating light in a field/frame interval in accordance with a charge accumulation interval of said image sensor, said brightness adjuster changing an overlapping interval of the irradiation interval and the charge accumulation interval by shifting a rotation-phase of said rotary shutter on the basis of the detected luminance level, so as to maintain a brightness of the object image at a proper brightness. 
 
   
   
     9. The apparatus for adjusting a brightness according to  claim 8 , further comprising a light source controller that is capable of selectively setting an intensity level of illuminating light to one of a normal level required for illuminating an object and a low-level, adjacent to zero level, said light source controller setting the normal level for the irradiation interval, and setting the low-level for another interval. 
   
   
     10. The apparatus for adjusting a brightness according to  claim 8 , wherein said light transmitting portion comprises a pair of aperture portions, said pair of aperture portions being opposite each other and each extending circumferentially for 90°. 
   
   
     11. The apparatus for adjusting a brightness according to  claim 8 , wherein said light transmitting portion comprises an aperture portion, said aperture portion extending circumferentially for 180°. 
   
   
     12. The apparatus for adjusting a brightness according to  claim 8 , wherein said light transmitting portion comprises R, G and B color filters extending circumferentially and spaced from one another at regular intervals. 
   
   
     13. The apparatus for adjusting a brightness according to  claim 8 , wherein said brightness adjuster changes an illumination time from a start to an end of the field/frame interval by shifting a rotation phase of said rotary shutter. 
   
   
     14. The apparatus for adjusting a brightness according to  claim 8 , wherein said brightness adjuster decreases the rotation speed of said rotary shutter in response to the detected luminance level exceeding a reference luminance level. 
   
   
     15. A method for adjusting a brightness of an object image in an electronic endoscope, comprising:
 detecting a luminance level of an object image on the basis of image-pixel signals that are read from an image sensor of a video-scope successively; 
 rotating a single rotary shutter that comprises a light-transmitting portion and a shield portion, such that the single rotary shutter rotates while the light-transmitting portion and the shield portion alternately cross a light-path of the illuminating-light; and 
 controlling the rotary shutter to adjust an irradiation interval of the illuminating light in a field/frame interval in accordance with a charge accumulation interval of the image sensor, the controlling comprising changing an overlapping interval of the irradiation interval and the charge accumulation interval by shifting a rotation-phase of the rotary shutter on the basis of the detected luminance level, so as to maintain a brightness of the object image at a proper brightness. 
 
   
   
     16. The method for adjusting a brightness according to  claim 15 , further comprising selectively setting an intensity level of illuminating light to one of a normal level required for illuminating an object and a low-level, adjacent to zero level, and setting the normal level for the irradiation interval and setting the low-level for another interval. 
   
   
     17. The method for adjusting a brightness according to  claim 15 , wherein the light transmitting portion comprises a pair of aperture portions, the pair of aperture portions being opposite each other and each extending circumferentially for 90°. 
   
   
     18. The method for adjusting a brightness according to  claim 15 , wherein the light transmitting portion comprises an aperture portion, the aperture portion extending circumferentially for 180°. 
   
   
     19. The method for adjusting a brightness according to  claim 15 , wherein the light transmitting portion comprises R, G, and B color filters extending circumferentially and spaced from one another at regular intervals. 
   
   
     20. The method for adjusting a brightness according to  claim 15 , wherein the controlling comprises changing an illumination time from a start to an end of the field/frame interval by shifting a rotation phase of the rotary shutter.